Device for Injecting Apportioned Doses of Liquid Drug

ABSTRACT

An injection device ( 1 ) for injecting apportioned doses of liquid drug. The injection device ( 1 ) includes a dose setting structure, an injection structure, a removable cap ( 15 ) and a cap receiving part ( 9 ) adapted to abut or engage with the cap ( 15 ) when the cap ( 15 ) is mounted on the injection device ( 1 ). The dose setting structure is operatively coupled to the cap receiving part ( 9 ) in such a manner that mounting and/or dismounting of the cap ( 15 ) on/from the injection device ( 1 ) causes the dose setting structure to set a dose. Thereby a correct dose of drug is automatically set during a cap on/cap off cycle. Since such a cycle is normally performed between subsequent injections, the number of steps required to be performed by the user is reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/842,337, filed Jul. 23, 2010 (Notice of Allowance received), which isa continuation of Ser. No. 12/864,279, filed Jul. 23, 2010 (U.S. Pat.No. 8,348,905, issued Jan. 8, 2013), which is a 35 U.S.C. §371 nationalstage application of International Patent Application PCT/EP2009/050797(published as WO 2009092807), filed Jan. 23, 2009, which claimedpriority of European Patent Application 08150533.1, filed Jan. 23, 2008;this application further claims priority under 35 U.S.C. §119 of U.S.Provisional Application 61/027,099, filed Feb. 8, 2008, the contents ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an injection device for injectingapportioned doses of liquid drug, such as for injecting doses of asingle fixed amount of drug, or for injecting doses of a limited numberof different amounts of drug. More particularly, the present inventionrelates to an injection device in which the number of operations to beperformed by a user is minimised. The injection device is particularlysuitable for self-injection by the user of a liquid drug, e.g. insulinfor treating diabetes.

BACKGROUND OF THE INVENTION

Within some therapy areas the tendency of a patient to adhere to theprescribed therapy is dependent on the simplicity of the specifictreatment regimen. For example, many people with type 2 diabetes arediagnosed with the disease at a relatively high age where they are lessprone to accept a treatment that intervenes too much with their normalway of living. Most of these people do not like constantly beingreminded of their disease and, as a consequence, they do not want to beentangled in complex treatment patterns or waste time on learning tooperate cumbersome delivery systems.

Basically, people with diabetes need to keep track of, and minimise,their glucose excursions. Insulin is a well-known glucose lowering agentwhich has to be administered parenterally to be effective in the body.The presently most common way of administering insulin is bysubcutaneous injections. Such injections have previously been performedusing a vial and a syringe, but in recent years so-called injectiondevices, or injection pens, have gained more and more attention in themarketplace. This is for one thing due to the fact that for many peoplethese injection devices are easier to handle, particularly as they donot require the user to carry out a separate filling procedure beforeeach injection.

In some prior art injection devices which are suitable forself-injection, the user has to set a desired dose using a dose settingmechanism of the injection device and subsequently inject the previouslyset dose using an injection mechanism of the injection device. In thiscase the dose is variable, i.e. the user must set a dose which issuitable in the specific situation each time a dose is to be injected.

Other prior art injection devices are adapted to inject a fixed doseeach time it is operated. In this case the user has to prepare theinjection device, thereby setting the fixed dose, using a dose settingor loading mechanism, and subsequently inject the dose using aninjection mechanism.

U.S. Pat. No. 4,973,318 discloses a disposable syringe comprising aprotective cap which is removably mounted over a first housing elementof the syringe. The cap is configured to abut a second housing elementwhile mounted in place on the first housing element. The protective capis engaged with the first housing element such that rotation of the capwith respect to the second housing element causes rotation of the firsthousing element with respect to the second housing element. Thisrelative rotation causes a variable dose to be set, i.e. the protectivecap is used when setting a dose. However, it is necessary for the userto perform the step of setting a dose as well as the step of injectingthe set dose.

U.S. Pat. No. 5,674,204 discloses a medication delivery pen having amedication cartridge, a pen body assembly and a cap. The pen bodyassembly includes a dose setting mechanism and a dose delivery mechanismthat are selectively disconnected and connected by attaching andremoving, respectively, the cap of the medication delivery pen. When thecap is attached to the medication delivery pen the user can easily dialin and correct the dialled in dosage and when the cap is removed themedication delivery pen is ready to dispense the dialled in dose. Thus,attaching/removing the cap to/from the medication delivery pen causes aclutch mechanism to be operated to switch the medication delivery penbetween a dose setting mode and an injection mode. Also in this deviceit is necessary for the user to perform the step of setting a dose aswell as the step of injecting the set dose.

An example from another medical device area, U.S. Pat. No. 7,302,948discloses a nasal applicator in which a drug container is able to slideback and forth in response to the cocking and actuation of a spring. Thedrug container is slided backwards when a cap is attached to the nasalapplicator. An abrupt stop during the forward movement of the drugcontainer causes a piston to move and eject a dose of the drug through adispensing nozzle.

U.S. Pat. No. 6,056,728 discloses an injection device which offersautomatic needle insertion. It includes an intermediate chamber betweenthe drug reservoir and the injection outlet for receiving a volume ofthe drug during preparation of the device for injection. The device hasa rather bulky construction which makes it less attractive to carryaround in e.g. a handbag.

It is desirable to provide an injection device which is simple to handleand which is intuitive and easy for the patient to learn how to use. Inparticular, it is desirable to provide an injection device which iscapable of administering a number of doses of liquid drug, while at thesame time requiring a minimum number of operations to be performed bythe user. It is also desirable to provide an injection device whichclearly indicates to the user when it is ready for injection and whenthe remaining volume of drug in the reservoir is insufficient to providea full dose, and which then automatically renders further activation ofthe injection mechanism impossible. It is further desirable to providean injection device which has a non-bulky design, so the user is nottempted to leave it at home instead of carrying it along during the day.

Some prior art injection devices offer so-called automatic delivery.These injection devices use energy from an internal energy source,typically a spring, to advance the piston in the reservoir. Automaticinjection devices intend to reduce the force required by the user toeject the drug out of the reservoir. An example of such an injectiondevice is found in U.S. Pat. No. 5,104,380.

In an automatic, spring-powered injection device where an engagementmember is retracted axially along a toothed piston rod when the deviceis readied for injection, it must be ensured that the spring is cockedand secured against release at the same time as the engagement membermoves into engagement with a dedicated tooth on the piston rod. If theengagement member has moved into engagement with a tooth on the pistonrod but the spring has not been secured against release, the device willdeliver an unintended dose. On the other hand, if the spring has beencocked and secured against release without the engagement member havingmoved into engagement with a tooth on the piston rod, no dose will bedelivered when the injection mechanism is activated.

It is therefore desirable to provide an automatic injection device withwhich the user is ensured that a dose is either set correctly, andsecured against delivery until the user activates the injectionmechanism, or not set at all.

In U.S. Pat. No. 6,193,698 a spring is used to bias a dosing button anda drive arrangement towards a proximal position in an injectionapparatus. During an injection the dosing button and the drivearrangement are pushed towards a distal position. To preventuncontrolled injections, a locking member prevents return movement ofthe dosing button and the drive arrangement against the biasing force ofthe spring. In order to release the dosing button the user must manuallypress a trigger button which is accessible only after manual placementof two sleeves in a “zero” position relative to each other.

It is desirable to provide an injection device which locks the dosingbutton in a distal position following an injection, and whichautomatically releases the dosing button and moves it axially back intoa proximal position when the injection device is readied for aninjection so the user can see that the device is handled properly.

EP 1 304 129 discloses an injection device which includes a mechanismfor automatically locking out the dose dial from an inadvertentinjection after the dial has been retracted to set a dose. The lockoutmechanism comprises an interference fit between flexible fingers formedin the dial and a groove in the device housing. These fingers must beable to withstand large compressive forces in order to prevent the dialfrom being depressed in case of misuse or accidental handling of thedevice.

US 20070135767 discloses another example of an injection device whichincludes a mechanism for preventing inadvertent depression of aninjection button.

It is desirable to provide an injection device which the user does notrisk inadvertently activating to eject a dose of drug while theprotective cap is still on and which at the same time does not require amechanical lock that is able to resist large forces.

It is further desirable to provide an injection device which is bothsafe and effective to use and safe to carry around.

Generally, when manufacturing injection devices which comprise a pistonrod adapted to move a piston in a reservoir to thereby expel drug out ofthe reservoir it is essential that the piston rod is in engagement withthe piston during the entire course of injection. If this is not thecase the user may risk injecting a smaller amount of drug than intended.However, it is for several reasons preferred that the drug is notpressurised in the reservoir when the user takes the injection deviceinto use for the first time. Injection devices are therefore oftenmanufactured in such a way that a small clearance is deliberatelyprovided between the piston rod and the piston to allow some play of thepiston rod during transportation. In case of variable dose injectiondevices, when taking the device into use for the first time, the usersets a small dose and ejects it into the air. This action primes theinjection device such that when a next dose is set the user is sure toinject the correct amount of drug, since the piston rod and the pistonare now connected. In some fixed dose injection devices the piston rodtravels a substantial distance each time a dose is injected. If the userin this case initially sets a dose and fires it into the air to primethe device, a substantial amount of drug may be wasted to thesurroundings. This is particularly unwanted if the drug is expensive.

It is therefore desirable to provide a fixed dose injection device withwhich a user can perform an initial priming without wasting anapproximately full dose of drug.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an injection device in whichthe number of operating steps required to be performed by the user isreduced as compared to similar prior art injection devices.

It is a further object of the invention to provide an injection devicewhich is intuitive and thereby easy to learn how to use.

It is an even further object of the invention to provide an injectiondevice in which the dose setting procedure is simplified as compared tosimilar prior art injection devices.

It is an even further object of the invention to provide an injectiondevice which clearly signals to the user when it is ready for aninjection.

It is an even further object of the invention to provide an injectiondevice which clearly signals to the user when the remaining amount ofmedicament in the reservoir is insufficient to provide another full doseand which automatically renders further use of the device impossible.

It is an even further object of the invention to provide an injectiondevice in which the injection means is automatically disabled when theprotective cap is mounted on the device and automatically enabled whenthe protective cap is dismounted from the device, thereby ensuring thatthe user do not risk involuntarily ejecting a dose of medicament intothe cap when for example carrying the device in a hand bag.

It is an even further object of the invention to provide an injectiondevice which automatically sets a correct dose, thereby eliminating therisk of a user setting an incorrect dose.

It is an even further object of the invention to provide an injectiondevice which is capable of injecting a predetermined dose and which hasan initial priming feature allowing the user to perform a first shotwith the injection device that results in an ejection of a smallervolume of drug than the predetermined dose.

In the following disclosure of the present invention, aspects andembodiments will be described which address one or more of the aboveobjects or which address objects apparent from the disclosure as well asfrom the description of exemplary embodiments.

Thus, according to a first aspect of the invention a mechanicalinjection device for injecting apportioned doses of liquid drug isprovided, the injection device comprising dose setting means beingoperable to set a dose, injection means being operable to inject apreviously set dose, a removable cap, and a cap receiving part adaptedto abut or engage with the cap when the cap is mounted on the injectiondevice, wherein the dose setting means is operatively coupled to the capreceiving part in such a manner that mounting and/or dismounting of thecap on/from the injection device causes the dose setting means to set adose.

The injection device may for example be of the kind which is able torepeatedly set and deliver a predetermined dose.

In the present context the term ‘mechanical injection device’ should beinterpreted to mean an injection device which is mechanically operatedas opposed to motor driven injection devices.

In the present context the term ‘liquid drug’ should be interpreted tomean a drug in a liquid state, such as, e.g., a solution or asuspension.

In the present context the term ‘predetermined dose’ should beinterpreted in such a manner that when the dose setting means isoperated a specific fixed dose is set, i.e. it is not possible to set anarbitrary dose. However, the predetermined dose may be variable in thesense that it may be possible to initially set the injection device to aselected dose, and the dose setting means will then set this selecteddose each time the dose setting means is operated. It should also benoted that the term ‘predetermined dose’ does not rule out that theinjection device has a priming function.

The injection device is preferably capable of injecting multiple dosesof liquid drug.

The dose setting means is the part of the injection device which isoperated when a dose is being set. Similarly, the injection means is thepart of the injection device which, when operated, is causing a set doseto be injected. The injection means often comprises a movable piston rodbeing adapted to cooperate with a piston arranged in a cartridgecontaining the liquid drug in such a manner that operation of theinjection means causes the piston rod to move in such a manner that thepiston is moved inside the cartridge in a direction which causes liquiddrug to be expelled from the cartridge via a needle arranged topenetrate a septum of the cartridge.

The injection device comprises a removable cap which may be adapted tocover a needle holding part of the injection device when the injectiondevice is not in use. Thereby the removable cap is capable of protectinga needle mounted on the needle holding part, preventing needle sticksand preventing accidental spilling of liquid drug. The cap can beremoved when it is desired to inject a dose, thereby uncovering theneedle holding part.

The cap receiving part is a part of the injection device which isadapted to receive and hold the removable cap when it is mounted on theinjection device. It may comprise means for retaining the cap, such as abayonet joint, a threaded portion, a snap lock, etc. The cap receivingpart may be adapted to receive the cap when the cap is mounted on theinjection device to cover the distal part of the injection device.Alternatively, the cap receiving part may be adapted to receive the capwhen the cap is mounted on the proximal part of the injection device.

The dose setting means is operatively coupled to the cap receiving part,i.e. performing specific operations of the cap receiving part affectsthe dose setting means. More particularly, the dose setting means andthe cap receiving part are coupled in such a manner that mounting and/ordismounting of the cap on/from the injection device causes the dosesetting means to set a dose. The dose setting means and the capreceiving part may be mechanically coupled, either directly or via oneor more intermediate parts, or they may be coupled in any other suitableway as long as specific operations of the cap receiving part affects thedose setting means in such a manner that the dose is set. Thus, the dosemay be set when the cap is mounted or when the cap is dismounted.Alternatively, the dose may be partly set when the cap is mounted, theremaining part of the dose being set when the cap is subsequentlydismounted. In any event, performing a cycle of operations comprisingmounting and dismounting the cap results in the dose being set by thedose setting means, preferably automatically.

The removable cap is normally positioned at the cap receiving part,preferably covering a needle holding part or a jet orifice, when theinjection device is not in use, and the cap is removed when it isdesired to inject a dose of drug by means of the injection device. Afterthe dose has been injected the cap is once again mounted at the capreceiving part. Thus, each time a dose is injected the cap has beenmounted and dismounted since the previous dose was injected. Since thedose setting means and the cap receiving part are coupled as describedabove, such a mounting/dismounting cycle of the cap automaticallyresults in a dose being set. Therefore, when the user has removed thecap in order to inject a dose, the dose is already set, and it is notnecessary for the user to perform additional operating steps in order toset the dose. Thereby the number of steps to be performed by the user isreduced. Furthermore, since the dose is automatically set, the risk ofintroducing errors during dose setting is reduced.

Thus, in one particular embodiment of the invention an injection devicefor administering apportioned doses of a liquid drug is provided, theinjection device comprising dose setting means operable to set a dose,injection means operable to inject the set dose, a removable cap, a capreceiving part adapted to abut or engage with the cap when the cap ismounted on the injection device, wherein the dose setting means isoperatively coupled to the cap receiving part in such a manner thatmounting and/or dismounting of the cap on/from the injection devicecauses the dose setting means to set a single dose.

In the present context, the term ‘to set a single dose’ should beinterpreted as outlined in the above, i.e. mounting the cap on, ordismounting the cap from, the injection device causes the dose settingmeans to set one dose which is deliverable upon operation of theinjection means. By such an arrangement it is therefore not possible toinject two consecutive doses without performing a cycle of mounting anddismounting the cap on/from the injection device. This constitutes asafety feature of the device since if it was possible to inject amultiple number of doses, such as the same dose a multiple number oftimes, without performing the cap mounting/dismounting cycle, the userwould have to keep count of how many times the injection means had beenoperated. This could lead to confusion and uncertainty regarding theactual dose delivered.

A substantially linear movement of the cap may cause the dose settingmeans to set the dose, i.e. the movement of the cap may involve asubstantially linear translation which causes the dose setting means toset the dose. According to this embodiment, the cap is mounted and/ordismounted in a substantially linear movement. In this case the cap ispreferably retained in the mounted position by means of a snap lock, abayonet joint or the like. According to this embodiment, the cap maymove an element in a substantially axial direction when it is mounted ordismounted. The movement of the element may cause the dose to be set,e.g. by storing energy in a spring member and/or by moving an injectionbutton in an axial direction.

Alternatively, or additionally, a rotational movement of the cap maycause the dose setting means to set the dose, i.e. the movement of thecap may involve a rotational movement which causes the dose settingmeans to set the dose. According to this embodiment, the cap ispreferably mounted and/or dismounted in a movement which is at leastpartly rotational, e.g. a purely rotational movement or a spirallingmovement. The cap may, in this case, be retained at the cap receivingpart by means of a threaded connection, a bayonet joint or the like. Therotational part of the movement may alone be responsible for setting ofthe dose, e.g. by causing an element of the injection device to rotatealong. For instance, in the case that the cap is retained by means of abayonet joint, the rotating part of the mounting or dismountingoperation may cause an element to rotate along. It may be envisaged thatthe cap is mounted in a substantially linear movement, pressing the cappast a threaded portion, and that the cap must be rotated along thethreaded portion in order to dismount the cap. In this case the rotatingpart of the dismounting movement may advantageously cause the dose to beset. This has the advantage that the dose is not set until immediatelyprior to the intended injection of the dose, and it can thereby beavoided that a loaded injection device must be carried in a pocket or ahandbag. Thereby the risk of accidentally ejecting the set doseprematurely in the cap is minimised. However, this could alternativelybe obtained by means of a suitable locking mechanism preventinginjection of the set dose until the cap has been removed.

As an alternative to the purely rotational movement, a combination of alinear and a rotational movement, i.e. a spiralling movement may causethe dose setting means to set the dose.

In a particular embodiment of the invention, mounting the cap on theinjection device causes an element to move axially with respect to thepiston rod to thereby move an engagement member along the piston rod toa more proximal position. Each time a dose is set by mounting the cap onthe injection device the engagement member is thus moved further alongthe piston rod towards the proximal end thereof.

In an exemplary embodiment of the invention an injection device foradministering apportioned doses of a liquid drug is provided, theinjection device comprising a proximal part and an opposite distal part,a cartridge adapted to hold the liquid drug and comprising a movablepiston, dose setting means operable to set a dose, injection meansoperable to inject the set dose and comprising a piston rod adapted tosequentially advance the piston in the cartridge, each sequentialadvancement corresponding to the set dose, a removable cap adapted tocover the distal part of the injection device, and a cap receiving partadapted to abut or engage with the cap when the cap is mounted on theinjection device, wherein the dose setting means is operatively coupledto the cap receiving part in such a manner that mounting and/ordismounting of the cap on/from the distal part of the injection devicecauses the dose setting means to set a dose. Since the distal part ofthe injection device is the part from which the drug is ejected out ofthe reservoir, the removable cap is adapted to cover and protect thedrug outlet.

The injection device may further comprise energy means connected to thedose setting means and the injection means in such a manner that energyis stored in the energy means during setting of a dose, and in such amanner that previously stored energy is released from the energy meansduring injection of a dose, thereby causing the dose to be injected.

The energy means may be a spring member which may be adapted to beloaded along its centre axis, e.g. by compressing the spring orelongating the spring. The spring member may be a compressible spring ora torsion spring. In the case that the spring member is a compressiblespring, the injection device may advantageously be operated in thefollowing manner. When the cap is either mounted on or dismounted fromthe cap receiving part a spring compressing element is moved, preferablyin an axial direction, thereby compressing the spring. The springcompressing element is locked in this position, thereby retaining thespring member in the compressed state. When the injection needle hasbeen inserted at a desired injection site, the injection button ispressed. This causes the spring compressing element to be moved out ofthe locked position, and the energy stored in the spring is therebyreleased in such a manner that it causes a piston rod to move whilepressing a piston of a cartridge forward, thereby causing a dose of drugto be injected from the cartridge, via the injection needle.

According to a second aspect of the invention an injection device isprovided comprising a housing, dose setting means operable to set adose, injection means operable to inject the set dose and comprising anat least partly toothed rod, a drive member adapted to undergo relativemotion with respect to the toothed rod when the dose setting means isoperated and to transmit a driving force to the toothed rod when theinjection means is operated, the drive member comprising an engagementelement adapted to engage with the toothed rod, guiding means adapted toguide the movement of the drive member and/or the toothed rod, andenergy means operatively coupled to the dose setting means and theinjection means and adapted to store and release energy fortranslational and rotational motion.

The drive member may be coupled with the energy means in such a mannerthat movement of the drive member causes the energy means to storeand/or release energy and, conversely, in such a manner that release ofenergy from the energy means causes the drive member to move. The energymeans may comprise a compression spring being rotationally pre-stressedto bias the drive member in a specific rotational direction.

When the dose setting means is operated to set a dose the drive memberwill undergo a relative motion with respect to the toothed rod wherebythe engagement element will be moved out of engagement with a tooth onthe toothed rod and moved along the toothed rod to pass a moreproximally positioned tooth. This relative motion is guided by theguiding means. The guiding means may form part of the housing or may bea separate element coupled to the housing. When the injection means issubsequently operated to inject the set dose the engagement member willengage the tooth it just passed and the drive member will move distallyin the housing while slaving the toothed rod. Also this motion is guidedby the guiding means.

Hence, in the present context the term ‘the dose setting means isoperated to set a dose’ should be interpreted to mean that the dosesetting means is operated to a degree where a dose is actually set. Justoperating the dose setting means does not necessarily lead to a dosebeing set, as will be clear from the below.

Further, in the present context the term ‘tooth’ should be interpretedto mean any lateral structural irregularity on the rod, such as e.g. aprotrusion or an indentation, capable of receiving an engagement elementand allowing for a mutual axial displacement of the rod and theengagement element.

In an exemplary embodiment of the invention the guiding means comprisesa structure which enables the drive member and the toothed rod toperform a purely translational relative motion during one part of therelative motion and to perform a combined translational and rotationalrelative motion during another part of the relative motion. In thisparticular embodiment the guiding means is provided with a longitudinalfirst guiding surface which is substantially parallel with the toothedrod and which enables the purely translational relative motion betweenthe drive member and the toothed rod. The guiding means is furtherprovided with a sloping second guiding surface which meets the firstguiding surface at a transition point and which enables the combinedtranslational and rotational relative motion between the drive memberand the toothed rod. The second guiding surface and the first guidingsurface are preferably mutually angled between 180° and 270°, morepreferably between 225° and 270°, and most preferably between 240° and270°. In any case the angle between the first guiding surface and thesecond guiding surface and the traversable dimension of the secondguiding surface constitute two parameters which should be fitted so thatwhen the drive member traverses the second guiding surface during dosesetting the drive member and the toothed rod perform a combinedtranslational and rotational relative motion during which the engagementelement passes a tooth on the toothed rod.

The energy means may comprise a compression spring being rotationallypre-stressed to constantly bias the drive member in a specificrotational direction. The spring may further be axially pre-stressed toconstantly bias the drive member in the distal direction of theinjection device. This means that when the drive member is traversingthe first guiding surface of the guide means it is exposed to the axialforce of the spring seeking to displace it distally in the injectiondevice. During dose setting the drive member may thus traverse the firstguiding surface against the force of the spring, while during injectionthe drive member may traverse the first guiding surface under the forceof the spring. Further, when the drive member is traversing the firstguiding surface it may be exposed to the rotational force of the spring.However, the drive member is prevented from being rotated in accordancewith a biasing rotational force of the spring when traversing the firstguiding surface. This is due to the first guiding surface being arrangedlongitudinally and substantially in parallel with the toothed rod.

The transition point denotes the position where the first guidingsurface and the second guiding surface meet, i.e. the point where thedrive member is transitioned from traversing the first guiding surfaceto traversing the second guiding surface, and vice versa. When the drivemember is traversing the second guiding surface it may be exposed toboth the axial and the rotational biasing forces of the spring. Sincethe second guiding surface is sloped these biasing spring forces enablea combined translational and rotational movement of the drive memberwith respect to the toothed rod. During dose setting the drive membermay traverse the second guiding surface under the rotational force ofthe spring, but against the axial force of the spring. During operationof the injection means the drive member may traverse the second guidingsurface against the biasing rotational force of the spring.

The spring and the sloping angle of the second guiding surface arepreferably dimensioned so that the biasing rotational force of thespring is able to move the drive member along the second guiding surfaceagainst the biasing axial force of the spring.

The guiding means is preferably provided with an abutting surfaceadapted to stop the combined translational and rotational movement ofthe drive member when the drive member is in a position where theengagement element has just passed a tooth on the toothed rod. In thisposition the spring is both cocked and secured against release since thebiasing rotational force of the spring is able to overcome the biasingaxial force of the spring and thereby retain the drive member in astabile stationary state.

The guiding means is further preferably provided with an abuttingsurface adapted to stop the translational movement of the drive memberduring injection, thereby indicating an end-of-dose position, i.e. aposition of the drive member corresponding to the complete delivery ofthe set dose. The actual dose delivered may be determined by thedistance between two consecutive teeth on the toothed rod. This distanceis greater than the axial distance travelled by the drive member alongthe first guiding surface of the guiding means, but smaller than thetotal axial distance travelled by the drive member following activationof the injection means, i.e. smaller than the combined axial dimensionof the first and the second guiding surfaces. The actual dose deliveredmay alternatively be determined by the total axial distance, which thedrive member travels following activation of the injection means.

The above described arrangement is particularly advantageous since whenthe user operates the dose setting means to set a dose the last part ofthe dose setting may be performed automatically by the injection device.This is due to the fact that during the first part of the dose settingthe user manually operates the dose setting means to move the drivemember proximally along the first guiding surface against the biasingtranslational force of the spring. If the spring is rotationallypre-stressed it constantly exerts a force on the drive member which maybias the drive member against the first guiding surface. Hence, in thiscase, as long as the drive member is guided by the first guiding surfaceit is prevented from rotating and it therefore performs a purelytranslational movement during which the engagement element is slidedalong the toothed rod. When the user has forced the drive member so farproximally that it reaches the transition point at the connectionbetween the first guiding surface and the second guiding surface thebiasing rotational force of the spring may begin rotating the drivemember and force it to travel along the second guiding surface until itreaches the stop at the abutting surface. Since the second guidingsurface is sloped the drive member will thereby be performing a combinedrotational and translational movement with respect to the toothed rod.The configuration of the first and second guiding surfaces may be suchthat the axial displacement which the drive member undergoes from thetransition point to the stop at the abutting surface moves theengagement element from a position just below, or distally of, a giventooth on the toothed rod to a position just above, or proximally of, thetooth. This ensures that when the injection means is operated theengagement element will be able to move into engagement with this toothand slave the toothed rod axially towards the distal end of theinjection device. During movement of the drive member along the secondguiding surface, the spring may release rotational energy while itstores translational energy. In that case, when the drive member reachesthe stop at the abutting surface the spring is cocked as well as securedagainst release until the next activation of the injection means.

As long as the dose setting means is manipulated in such a way that thedrive member travels along the first guiding surface no dose is set, andif the user ends the manipulation of the dose setting means before thedrive member has reached the transition point the biasing translationalforce of the spring may just return the drive member to the startingpoint, i.e. the end-of-dose position. However, when the dose settingmeans is manipulated to an extent where the drive member reaches thetransition point the spring may take control of the remaining part ofthe dose setting and ensure that the dose is actually being set, i.e.that the engagement element actually passes the intended tooth on thetoothed rod, and that the drive member is retained in a stabilestationary state from which it can not be moved unless the injectionmeans is manipulated. In that case, the last part of the dose settingprocedure is carried out automatically by the injection device and theuser does not have any options of intervention.

When the user operates the injection means to inject the set dose thedrive member may be initially forced along the second guiding surfaceagainst the biasing rotational force of the spring. At some point duringthis movement the engagement element will move into engagement with atooth on the toothed rod. When the drive member reaches the transitionpoint the biasing translational force of the spring may move the drivemember and the toothed rod axially in the distal direction until thedrive member meets the abutting surface.

The toothed rod may be operatively coupled with a drug containingreservoir in the injection device in such a manner that the axialdistance travelled by the toothed rod correlates with the actual dosedelivered from the reservoir. The drug containing reservoir may be arigid reservoir, such as a cartridge, comprising an axially moveablepiston and the toothed rod may be operatively coupled to the reservoirvia the piston. Alternatively, the drug containing reservoir may be aflexible reservoir which is adapted to undergo a controlled deformationwhen the toothed rod is moved axially in the injection device. In anycase, the axial movement of the toothed rod may cause a volume reductionof the drug containing reservoir corresponding to the delivered dose.

The dose setting means may be operated by pulling the dose button in aproximal direction away from the housing. Alternatively, the dosesetting means may be operated as described in the following. Theinjection device may further comprise a removable cap and a capreceiving part adapted to abut or engage with the cap when the cap ismounted on the injection device. The dose setting means may beoperatively coupled with the cap receiving part in such a manner thatmounting the cap on the injection device causes the drive member to moveaxially along the toothed rod while being guided in this movement by theenergy means and the geometry of the guiding means, as described above.In this particular embodiment, mounting the cap on the injection devicecauses the injection device to automatically set a dose. The guidingmeans may be configured so that each time the cap is mounted on theinjection device the drive member travels the same distance proximallyand each time the injection means is activated the drive member travelsthe same distance distally, in which case the injection device is afixed dose delivery device. However, the guiding means and/or thetoothed rod may alternatively, or additionally, be configured so that itis possible to pre-calibrate the zero dose position before a dosesetting, thereby in practice providing a variable dose delivery devicecapable of delivering a limited number of different doses of drug. Thiscould for example be implemented by providing means for regulating theaxial dimension of the first guiding surface.

The energy means may comprise a compression spring being rotationallypre-stressed as described above. However, other suitable energy meansmay be used such as for example two or more springs each being able toprovide a part of the energy needed for translational and rotationalmotion, e.g. a compression spring capable of providing energy fortranslational motion and a torsion spring capable of providing energyfor rotational motion, an axially compressible torsion rod or anarrangement comprising a tension spring.

According to a third aspect of the invention an injection device foradministering predetermined doses of liquid drug is provided comprisingdose setting means operable to set a dose, injection means operable toinject the set dose and comprising an at least partly toothed rod, and adrive member adapted to undergo relative motion with respect to thetoothed rod during dose setting and to transmit a driving force to thetoothed rod during injection, wherein the injection device has a primingfeature which allows the user to prime the injection device withoutejecting an approximately full predetermined dose.

The priming feature may be implemented by providing guiding means asdescribed in connection with the second aspect of the invention, theguiding means further comprising a second longitudinal guiding surface.This second longitudinal guiding surface may be identical to theabutting surface adapted to stop the movement of the drive member alongthe sloping ramp surface during dose setting. Alternatively, it may beanother longitudinal surface being physically connected to the slopingramp surface. In any case, the second longitudinal guiding surface ispreferably connected to a support shelf in such a way that before theuser takes the injection device into use for the first time, such aswhen the injection device is delivered from the manufacturer, the drivemember rests on the support shelf and when the user performs the veryfirst operation of the injection means, the drive member isautomatically caused to travel the second longitudinal guiding surfaceto take in a position on the sloping ramp surface. In case the injectiondevice further comprises energy means being operatively coupled to thedose setting means and the injection means and being adapted to storeand release energy for translational and rotational motion when the userperforms this first operation of the injection means the energy meansmay be activated to execute the initial movement of the drive member.

The longitudinal dimension of the second longitudinal guiding surface issmaller than the longitudinal dimension of the first guiding surfacewhich guides the drive member between the transition point and the endof dose position. This means that the initial axial movement of thedrive member is smaller than the axial movement it undergoes duringregular injection. In other words, since the drive member slaves thetoothed rod during injection the toothed rod is displaced axially asmaller distance upon the initial activation of the injection means thanupon a subsequent activation of the injection means leading to thedelivery of a set dose. Thereby it is possible to perform an initialpriming of the injection device without wasting an amount of drugapproximately equal to a predetermined dose.

The injection device may be provided with a tamper band which the usercan pull off to start the priming shot. This tamper band may e.g. beplaced at the distal end of the housing or just distally of theinjection button. Alternatively to the user pressing the injectionbutton to perform the initial priming, the priming may be activated byturning the injection button clockwise or anti-clockwise a certainnumber of degrees to remove the slider from the initial shelf position.

According to a fourth aspect of the invention a mechanical injectiondevice for injecting apportioned doses of liquid drug is provided, theinjection device comprising dose setting means being operable to set adose, injection means being operable to inject a previously set dose, aninjection button being operatively coupled to the dose setting means andthe injection means and being axially moveable between a first positionin which a dose is set and the injection device is ready for injectionand a second position in which the injection means has been activated toinject the set dose, and retaining means for retaining the injectionbutton in the second position upon activation of the injection means toinject the set dose. When the user removes his/her finger from theinjection button after an injection the injection button will thus stayin the second position, thereby signalling to the user that theinjection device is not yet ready for another injection.

In the present context the term ‘a second position in which theinjection means has been activated to inject the set dose’ should beinterpreted to mean a position where the injection means has beenactivated to a degree allowing for the complete set dose to be injected.

The injection device comprises a proximal part and an opposite, distalpart, and it is preferably of an elongated shape, defining a generalaxis which in the abstract bridges the proximal part and the distalpart. In the present context, an ‘axially moveable’ or ‘axiallydisplaceable’ element should thus be interpreted as an element which ismoveable or displaceable along the general axis of the injection device.

The retaining means may be operatively coupled to the dose setting meansin such a manner that when the dose setting means is operated to set adose the retaining means is automatically disabled. This will enable theinjection button to move from the second position back to the firstposition. In a particular embodiment, when the dose setting means isoperated to set a dose the injection button is automatically moved fromthe second position to the first position, whereby the injection devicesignals to the user that it is ready for injection.

The second position may be a position in which the injection button isfully depressed in or against the housing and in which only the top partor the push surface of the injection button can be seen and/or touchedby the user. The first position may, conversely, be a position in whichthe injection button clearly protrudes from the housing. Preferably, theaxial distance which the injection button travels between the firstposition and the second position is sufficiently large to provide aclear indication of whether the injection device is ready for injectionor not.

When the dose setting means is operated to set a dose, the injectionbutton may be moved from the second position to the first position by aforce transmitting member abutting or engaging with the injection buttonin such a manner that a translational, rotational or spiralling movementof the force transmitting member causes the movement of the injectionbutton. The injection button may be moved substantially linearly, i.e.non-rotationally, between the first position and the second position.Alternatively, or additionally, the movement may involve a rotation ofthe injection button.

The retaining means holding the injection button in the second positionwhen the injection means has been activated to inject the set dose maycomprise a simple friction fit between the injection button and thehousing or the force transmitting member, e.g. between the exterior ofthe injection button and the interior of the housing. Alternatively, oradditionally, the retaining means may comprise a snap fit between theinjection button and the housing or the force transmitting member. Theinjection button may comprise a catch member adapted to engage with alocking geometry on the housing, e.g. on the interior of the housing.Conversely, the housing may be provided with a catch member adapted toengage with a locking geometry on the injection button. During injectionwhen the injection button reaches the second position the catch membermoves into engagement with the locking geometry and retains theinjection button from reverse movement. During operation of the dosesetting means the engagement may be released by another forcetransmitting member acting to move the catch member away from thelocking geometry.

Energy means may act on the injection button to bias the injectionbutton towards the first position. In this case, disabling the retainingmeans may cause the energy means to automatically release energy formoving the injection button to the first position. In an exemplaryembodiment, the energy means comprises a spring being compressed duringinjection by the movement of the injection button from the firstposition to the second position. Disabling the retaining means whenoperating the dose setting means to set a dose causes the spring to pushthe injection button back to the first position, thereby indicating thata dose has been properly set and that the injection device is ready forinjection.

In a particular embodiment an injection device for administeringapportioned doses of a liquid drug is provided comprising a reservoiradapted to hold the liquid drug and comprising a moveable piston, dosesetting means being operable to set a dose, injection means beingoperable to inject a previously set dose and comprising a piston rodadapted to sequentially advance the piston in the reservoir, eachsequential advancement corresponding to the set dose, an injectionbutton being operatively coupled to the dose setting means and theinjection means and being axially moveable between a first position inwhich a dose is set and the injection device is ready for injection anda second position in which the injection means has been activated toinject the set dose, retaining means for retaining the injection buttonin the second position upon activation of the injection means to injectthe set dose, a removable cap, and a cap receiving part adapted to abutor engage with the cap when the cap is mounted on the injection device,wherein the dose setting means is operatively coupled to the capreceiving part in such a manner that mounting the cap on the injectiondevice causes the dose setting means to substantially simultaneously seta dose, disable the retaining means, and move the injection button fromthe second position to the first position.

In a further embodiment an injection device is provided comprising avariable volume reservoir, dose setting means operable to set a dose,injection means operable to inject the set dose and comprising a pistonrod adapted to cause a volume reduction of the reservoir, a drive memberadapted to perform relative translational and rotational motion withrespect to the piston rod during dose setting and to transmit a drivingforce to the piston rod during injection, a removable cap, a capreceiving part adapted to abut or engage with the cap when the cap ismounted on the injection device, an injection button operatively coupledto the dose setting means and the injection means and axially moveablebetween a first position in which a dose is set and the injection deviceis ready for injection and a second position in which the injectionmeans has been activated to inject the set dose, and energy meansoperatively coupled to the dose setting means and the injection meansand adapted to store and release energy for translational and rotationalmotion, wherein the piston rod comprises a structural element adapted toengage with the drive member to prevent the drive member from rotatingduring operation of the dose setting means when the remaining amount ofdrug in the reservoir is insufficient to provide another full dose,thereby providing an end-of-contents indication.

By such an arrangement, when the piston has been advanced to a pointwhere an insignificant or insufficient amount of drug is left in thereservoir the drive member is still able to move axially along thepiston rod during dose setting, but it is prevented from rotating withrespect to the piston rod. In case mounting the cap on the injectiondevice affects the dose setting means by causing the drive member moverelative to the piston rod, it is thus still possible to mount the capon the injection device. However, an axial displacement alone will notcause a dose to be set, and the device is therefore rendered impossibleto use for further injections.

As described above, the injection button may be automatically moved fromthe second position to the first position when the dose setting means isoperated to set a dose. However, when the dose setting means is operatedwithout a dose actually being set, the injection button will not move tothe first position, and the above arrangement will therefore signal tothe user mounting the cap on the cap receiving part after injection ofthe last dose that no further doses remain in the injection device.

The structural element provided on the piston rod may be a bead, ahammerhead construction or another configuration suited for engagementwith the drive member in order to prevent the drive member from rotatingrelative to the piston rod. In case the piston rod is a toothed rod, thestructural element may advantageously be provided at the proximal end ofthe piston rod, e.g. to rotationally lock the drive member after passageand activation of the most proximally positioned tooth on the pistonrod.

According to a fifth aspect of the invention an injection device isprovided which comprises a locking mechanism preventing injection of aset dose. Such a locking mechanism is preferably used for preventingthat a set dose is accidentally expelled before it is intended to injectthe dose, e.g. before a needle or a jet nozzle has been appropriatelypositioned at a suitable and desired injection site. This isparticularly useful in the case that mounting of the cap causes the dosesetting means to set a dose, since in this case some time will elapsebetween setting the dose and injecting it, and it may very well benecessary to carry the injection device along during this time interval,e.g. in a pocket or a handbag.

The locking mechanism may be automatically activated when the cap ismounted on the injection device. According to this embodiment, mountingthe cap may advantageously result in setting the dose as well asactivating the locking mechanism. Alternatively, the locking mechanismmay be manually and/or separately operable, or it may be automaticallyactivated by other suitable actions than mounting the cap.

Thus, according to an exemplary embodiment an injection device foradministering apportioned doses of a liquid drug is provided comprisinga variable volume reservoir adapted to hold the liquid drug, dosesetting means operable to set a dose, injection means operable to injectthe set dose, a removable cap, a cap receiving part adapted to abut orengage with the cap when the cap is mounted on the injection device,wherein the injection means is operatively coupled to the cap receivingpart in such a manner that mounting the cap on the injection devicedisables the injection means, thereby preventing an ejection of drugfrom the reservoir. This type of arrangement is advantageous since theuser is prevented from risking inadvertently activating the injectionmeans when e.g. carrying the injection device in a pocket or a handbag.

According to one embodiment, the locking mechanism must be separatelyswitched to an unlocking state prior to injection of a set dose. Thismay be performed manually and/or separately. Alternatively, the lockingmechanism may be automatically switched to the unlocking state when thecap is dismounted. In the case that mounting the cap activates thelocking mechanism and dismounting the cap switches the locking mechanismto the unlocking state, the cap may be regarded as forming part of thelocking mechanism. This embodiment is very safe, since the lockingmechanism is automatically activated and deactivated, and therefore theuser does not have to consider this or remember to activate/deactivatethe locking mechanism.

The reservoir may be a rigid cartridge comprising an axially moveablepiston or it may be a flexible reservoir capable of undergoingcontrolled volume reduction. The injection means may comprise an axiallymoveable piston rod being adapted to act on the reservoir, eitherdirectly or via a coupling device, to reduce the volume of thereservoir, causing drug to be expelled therefrom. Mounting the cap onthe cap receiving part may affect the injection means directly orindirectly by affecting an associated element. In any case, the cap,preferably the edge of the cap, affects the injection means mechanicallyin such a way that the injection means is incapable of being activatedeven if the user applies a very large force to the injection device.

The injection device may comprise a drive member adapted to slave thepiston rod during forward axial movement in the injection device, i.e.during movement towards the distal end of the device. In that case whenmounted on the cap receiving part the cap may physically block the drivemember from axial forward movement, e.g. through abutting surfaces. Thecap may, however, at the same time allow rotational movement of thedrive member.

In a particular embodiment the injection device further comprisesguiding means adapted to guide the movement of the drive member and/orthe piston rod, and an injection button operatively coupled to the dosesetting means and the injection means and axially moveable between afirst position corresponding to a position in which the dose is set anda second position corresponding to a position in which the injectionmeans has been activated to inject the set dose, wherein the injectionbutton is able to perform substantially unimpeded movement from thefirst position to the second position and back to the first positionwhen the cap is mounted on the injection device. In other words, theinjection button can be manipulated, e.g. depressed, while the cap ismounted on the device. Such an arrangement allows for an injectiondevice which is secured against premature activation of the injectionmechanism, without incorporating a mechanical lock capable ofwithstanding large forces being applied to the injection button, e.g. asa result of the user playing with, mishandling or dropping the device.

If the guiding means comprises a first longitudinal guiding surface anda second sloping guiding surface, as described in connection with thesecond aspect of the invention, this may be implemented by arranging thedrive member such that a part of the drive member abuts with the capedge when the cap is mounted on the injection device. The cap therebyblocks the drive member from moving axially and the piston rod is thusalso prevented from moving axially, in which case no dose can be ejectedfrom the reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in further detail with reference tothe accompanying drawings in which

FIG. 1 is a cross sectional view of an injection device according to afirst embodiment of the invention in an unloaded state,

FIG. 2 is a cross sectional view of the injection device of FIG. 1 in aloaded state,

FIG. 3 is a perspective view of an injection device according to asecond embodiment of the invention,

FIG. 4 is a perspective view of the injection device of FIG. 3 with someparts removed,

FIG. 5 is a detail of the injection device of FIGS. 3 and 4,

FIG. 6 is a cross sectional view of an injection device according to athird embodiment of the invention.

FIG. 7 is a cross sectional view of an injection device according to afourth embodiment of the invention,

FIG. 8 is a cross sectional perspective view of the housing of theinjection device, showing a guiding means in detail,

FIG. 9 is a perspective view of the housing of the injection device,showing the position of the guiding means in the housing,

FIG. 10 a and FIG. 10 b show the front side, respectively the back sideof a piston rod of the injection device,

FIG. 11 is a perspective view of a drive member of the injection device,

FIG. 12 is a two-dimensional representation of the guiding means and thedrive member, showing the drive member in two different positions withrespect to the guiding means,

FIG. 13 is a two-dimensional representation of guiding means furthercomprising a support shelf to enable initial priming,

FIG. 14 is a perspective view of a push button of the injection device,

FIG. 15 is a perspective view of a coupling element of the injectiondevice,

FIG. 16 is a perspective view of a spring retaining means of theinjection device,

FIG. 17 is a perspective view showing an assembly of the drive member, aspring, and spring retaining means,

FIG. 18 is a perspective view illustrating the functional connectionbetween the push button and the drive member,

FIG. 19 is a perspective view of the injection device with the housingremoved, showing an interaction between the drive member and theprotective cap,

FIG. 20 is a perspective view of an end-of-contents mechanism in theinjection device,

FIG. 21 is a cross sectional view of an injection device according to afifth embodiment of the invention,

FIG. 22 is a perspective view of a guiding means seen from the side,

FIG. 23 is a perspective view of a guiding means seen from the distalend,

FIG. 24 is a perspective view of a drive member,

FIG. 25 is a perspective view of a push button,

FIG. 26 is a perspective view illustrating the functional connectionbetween the push button and the drive member,

FIG. 27 is a perspective view showing the engagement between the drivemember and a piston rod,

FIG. 28 is a perspective view showing an assembly of the piston rod, thedrive member, the guiding means, and a spring, in a situation where thedrive member rests on the dose shelves of the guiding meanscorresponding to a loaded condition of the injection device,

FIG. 29 is a perspective view of an end-of-contents mechanism in theinjection device,

FIG. 30 is a perspective view of the injection device with the housingremoved, showing an interaction between the drive member and theprotective cap,

FIG. 31 is a cross sectional view of an injection device according to asixth embodiment of the invention, and

FIGS. 32 a-c show a push button release mechanism of the injectiondevice in detail.

In the figures like structures are mainly identified by like referencenumerals.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a cross sectional view of an injection device 1 according to afirst embodiment of the invention. In FIG. 1 the injection device 1 isshown in an unloaded state, i.e. a dose has not yet been set.

The injection device 1 comprises a housing 2, a cartridge holding part 3having a cartridge 4 arranged therein, and an injection button 5. At adistal end of the cartridge holding part 3 an injection needle 6 isattached. A piston rod 7 is arranged in abutment with a piston 8arranged in an interior part of the cartridge 3 in such a manner thatmoving the piston rod 7 in a distal direction will cause the piston 8 tomove in a distal direction, thereby causing liquid drug from thecartridge 4 to be expelled via the injection needle 6.

When a user has completed an injection a cap (not shown in FIG. 1) ismounted on the injection device 1 at cap receiving part 9 in such amanner that the injection needle 6 is covered. When the cap is mountedat the cap receiving part 9 it pushes against slider 10, thereby movingit in a proximal direction. This causes spring 11 to be compressed,thereby storing energy in the spring 11, and moves snap arms 12 in aproximal direction to a position beyond protrusions 13 arranged on thehousing 2. The protrusions 13 ensure that the snap arms 12 are retainedin this position.

The slider 10 is connected to the piston rod 7 via teeth (not shown)formed on the piston rod 7 and a teeth engaging part 14 formed on theslider 10. The teeth and the teeth engaging part 14 are arranged in sucha manner that the teeth engaging part 14 is allowed to pass over theteeth when the slider 10 is moved in a proximal direction relative tothe piston rod 7, but the piston rod 7 must move along with the slider10 when the slider 10 is moved in a reverse direction. Thus, moving theslider 10 in a proximal direction as described above causes the slider10 to move relative to the piston rod 7, the moved distancecorresponding to a predetermined dose, since the piston rod 7, andthereby the piston 8, will be moved along the same distance when theslider 10 is subsequently moved in a reverse direction.

Furthermore, the movement of the slider 10 in a proximal direction asdescribed above causes the injection button 5 to be moved in a proximaldirection, i.e. causing the injection button 5 to protrude from thehousing 2, thereby indicating to a user that the injection device 1 hasbeen loaded, i.e. a dose has been set.

FIG. 2 is a cross sectional view of the injection device 1 of FIG. 1 ina loaded state. In FIG. 2 a cap 15 has been mounted on the injectiondevice 1 at the cap receiving part 9. It is clear that the injectionbutton 5 has been moved in a proximal direction as compared to theposition shown in FIG. 1. It is also clear that the snap arms 12 havebeen moved in a proximal direction beyond the protrusions 13, and thatthe protrusions 13 retain the snap arms 12 in this position.

When it is desired to inject the set dose, the user removes the cap 15,thereby uncovering the injection needle 6, and inserts the injectionneedle 6 at a suitable injection site. The injection button 5 is thenpushed in a distal direction, i.e. towards the housing 2 and theposition shown in FIG. 1. This causes pushing surfaces 16 to push snaparms 12 towards the centre of the injection device 1, thereby releasingthem from the protrusions 13. Accordingly, the slider 10 is allowed tomove in a distal direction, and the energy stored in the spring 11during setting of the dose will cause this movement to take place. Dueto the engagement between the teeth of the piston rod 7 and the teethengaging part 14 of the slider 10, the piston rod 7 is moved along.Thereby the piston 8 is also moved in a distal direction, therebycausing the predetermined dose to be expelled from the cartridge 4 viathe injection needle 6.

When the injection has been completed, the cap 15 is once again mountedon the injection device 1 at the cap receiving part 9, thereby causing anew dose to be set as described above. It should be noted that since theslider 10 is moved the same distance each time the cap 15 is mounted onthe injection device 1, the set dose is a predetermined, fixed dose.

FIG. 3 is a perspective view of an injection device 100 according to asecond embodiment of the invention. A housing 102 and an injectionbutton 105 are visible, and a cap 115 is mounted on the injection device100. Since the injection button 105 is positioned relatively close tothe housing 102, it can be seen that the injection device 100 is notloaded, i.e. a dose has not been set.

FIG. 4 is a perspective view of the injection device 100 of FIG. 3. Forthe sake of clarity, some of the parts, notably the cap and the housing,have been removed. This allows the cartridge holding part 103 and theinjection button 105 to be seen. The injection device 100 of FIGS. 3 and4 is preferably operated in the following manner. When it is desired toinject a dose, the cap 115 is removed from the injection device 100 byrotating the cap 115 relative to the housing 102, thereby uncovering aninjection needle (not shown). The cap 115 engages the cartridge holdingpart 103 via teeth 117 arranged at the cap receiving part 109 in such amanner that when the cap 115 is rotated, the cartridge holding part 103is rotated along. Rotating the cartridge holding part 103 in this mannercauses track portion 118, which is actually a part of the cartridgeholding part 103, to rotate. An inclined portion of the track of thetrack portion 118 engages a protrusion (not shown) formed on an innerpart of the housing, and thereby the rotation of the track portion 118causes the track portion 118 to be moved axially in a proximal directionrelative to the housing.

Furthermore, rotating the cartridge holding part 103 causes the pistonrod 107 to rotate. The injection button 105 is connected to a threadformed on the piston rod 107, and therefore rotation of the piston rod107 results in a prolongation of the piston rod 107/injection button 105assembly. As the piston rod 107 is not allowed to move in a distaldirection, this prolongation causes the injection button 105 to move ina proximal direction, i.e. out of the housing. Thereby the injectiondevice 100 is loaded.

Finally, the axial movement of the track portion 118 causes the cap 115to be pushed away from the injection device 100.

After the cap 115 has been removed and the injection device 100 has beenloaded as described above, the injection needle is inserted at asuitable injection site. The injection button 105 is then pushed in adistal direction, i.e. towards the housing 102. Due to axial lockingbetween the injection button 105 and the piston rod 107 this movementresults in axial movement of the piston rod 107, and thereby druginjection.

When the injection has been completed, the cap 115 is once again mountedon the injection device 100. This is done by pushing the cap 115 ontothe injection device 100 in a substantially axial movement.Simultaneously, the injection button 105 must be pushed in a distaldirection in order to properly fit the cap 115 onto the injection device100.

FIG. 5 is a detail of FIG. 4, in which the cap receiving part 109, theteeth 117 and the track portion 118 are seen more clearly.

FIG. 6 is a cross sectional view of an injection device 200 according toa third embodiment of the invention. The injection device 200 is in aloaded state. The injection device 200 operates in a manner similar tothe injection device 1 shown in FIGS. 1 and 2. However, in this caseenergy is not stored in a spring, and the user has to manually press theinjection button 205 home in order to expel a set dose.

When an injection has been completed, the cap 215 is mounted on theinjection device 200 at the cap receiving part 209. The cap 215 pushesagainst slider 210, thereby moving it in a proximal direction, theslider 210 thereby pushing the injection button 205 in a proximaldirection, i.e. away from the housing 202 to the position shown in FIG.6.

The slider 210 and the piston rod 207 are engaged via teeth 219 formedon the piston rod 207 and teeth engaging parts 214 formed on the slider210. The teeth 219 and the teeth engaging parts 214 are arranged in sucha manner that the teeth engaging parts 214 are allowed to pass over theteeth 219 when the slider 210 is moved in a proximal direction relativeto the piston rod 207, and the piston rod 207 must be moved along whenthe slider 210 is moved in a reverse direction. Accordingly, moving theslider 210 in a proximal direction as described above, results in theslider 210 moving relative to the piston rod 207. The distance movedcorresponds to a predetermined dose as described above.

When it is desired to inject the set dose, the user removes the cap 215,thereby uncovering the injection needle 206, and the injection needle206 is inserted at a suitable injection site. The injection button 205is then pushed in a distal direction, i.e. towards the housing 202. Thiscauses the slider 210 to move in a distal direction, and due to theengagement between the teeth 219 and the teeth engaging parts 214, thepiston rod 207 is moved along. Thereby the piston 208 is also moved in adistal direction, and the set dose of drug is expelled via the injectionneedle 206.

FIG. 7 is a cross sectional view of an injection device 300 according toa fourth embodiment of the invention. The injection device 300 generallycomprises a housing 302 and a cartridge holding part 303 for supportinga cartridge 304 which contains the liquid drug. The liquid drug ispositioned between a piston 308, which is capable of moving axially inthe cartridge 304, a tubular cartridge wall 340, and a self-sealingseptum 342 covering a drug outlet 341 through which the liquid drug isintended to flow when the piston is advanced in the cartridge 304 andwhen an injection needle (not shown) is attached to the drug outlet 341via a needle hub interface 343. A cap 315 is mounted on a cap receivingpart 309 in the housing 302, whereby it protects the cartridge 304 andcovers the drug outlet 341. An injection button 305 being capable ofreciprocating axial motion with respect to the housing 302 is shown in aposition where it protrudes from the distal end of the housing 302. Thisindicates that the injection device 300 is in a loaded state, i.e. thata dose has been set and that the injection device 300 is ready toperform an injection (upon removal of the cap 315). This will beexplained in greater detail below.

A piston rod 307 is attached to the piston 308 via a piston rod foot 347and operatively coupled to the injection button 305 such that when thecap 315 is off, an injection needle has been attached to the needle hubinterface 343, and the injection button 305 is pressed against thehousing 302 the piston rod 307 will advance axially through the housing302 a certain distance, thereby displacing the piston 308 in thecartridge 304 an equivalent distance to inject a desired amount of drugthrough the outlet 341.

The movement of the piston rod 307 is realised through a coupling ring330 being in engagement with a helical track 351 in the injection button305, and a driver 310 which is in engagement with the coupling ring 330and which is adapted to engage with, and transmit a driving force to,the piston rod 307. The driver 310 is powered by a spring 311 which is atorsionally pre-tensioned compression spring capable of storing andreleasing energy for both translational and rotational motion. One endof the spring 311 is retained in a spring base 360 and the other end ofthe spring 311 is in engagement with the driver 310 in such a way thatthe spring 311 and the driver 310 are able to interchange both forcesand torques. The driver 310 is thus capable of performing bothtranslational and rotational motion relative to the housing 302. Thespring 311 may for example be torsionally pre-tensioned duringassemblage of the injection device 300, e.g. by mutually twisting itstwo end parts a half or a full turn. When the cap 315 is dismounted fromthe injection device 300, the movement of the driver 310 is guided by aguide member 320.

The housing 302 has two radially opposite apertures 361, each adapted toreceive a hook 362 provided on the spring base 360 to thereby retain thespring base 360 from translational as well as rotational movementrelative to the housing 302. The housing 302 further has a window 399useable for inspection of the current position of the driver 310 in theinjection device 300.

FIG. 8 is a cross sectional perspective view of the housing 302, whichshows the guide member 320 in more detail. For the sake of clarity theproximal end 344 of the cartridge holding part 303 has been removed fromthe figure. The guide member 320 comprises a dose shelf 323 adapted tosupport and guide the driver 310 during the second part of the dosesetting and the first part of the injection. A longitudinal guidesurface 324 leads from the dose shelf 323 to an end of dose stop 325.The dose shelf 323 is a helical ramp segment which extendscircumferentially from a connection with the longitudinal guide surface324 to a longitudinal stop surface 322. A click finger 326 is providedon the guide member, the click finger 326 having a tip 327 forengagement with the piston rod 307.

FIG. 9 is a perspective view of the housing 302 as seen from the distalend. It shows the position of the guide member 320 within the housing302. Again, for the sake of clarity the proximal end 344 of thecartridge holding part 303 has been removed from the figure. The guidemember 320 is a generally tubular structure positioned concentricallywith the housing 302 and connected to the housing 302 via a number ofspacers 386. This connection to the housing 302 provides a tubularclearance 389 between the outer wall 329 of the guide member 320 and theinside of the housing 302. Some of this tubular clearance is, however,taken up by the tubular proximal end 344 of the cartridge holding part303. The cap receiving part 309 comprises the remaining part of thetubular clearance 389 and a distal housing edge 385. A central bore 380is provided allowing passage of the piston rod 307 through the guidemember 320. The central bore 380 is adapted to guide axial movements ofthe piston rod 307.

FIG. 10 a shows a first side of the piston rod 307. A number of teeth319 are distributed along the piston rod 307, the distance between twoconsecutive teeth 319 being constant throughout the entire distribution.The teeth 319 are adapted for engagement with the driver 310 during doseinjection where the driver 310 engages a tooth 319 and slaves the pistonrod 307 in a forward motion. At its proximal end the piston rod 307 isprovided with a stop face 393 adapted to restrict the movement of thedriver 310 in an end-of-content situation.

FIG. 10 b shows a second side of the piston rod 307. On this side anumber of smaller teeth 396 are distributed, the distance between twoconsecutive teeth 396 equalling the distance between two consecutiveteeth 319 on the first side of the piston rod 307. Between twoconsecutive teeth 396 a number of even smaller teeth 395 aredistributed, the distance between two consecutive teeth 395 beingconstant throughout the distribution. The teeth 395 and 396 are intendedto be overridden by tip 327 of click finger 326 during advancement ofthe piston rod 307 through the central bore 380. At its proximal end thepiston rod 307 is provided with a longitudinal track 394 adapted torestrict the movement of the driver 310 in an end-of-content situation,preferably co-acting with stop face 393.

FIG. 11 is a perspective view of the drive member 310, generallycomprising a tubular body 370 having two radially opposite longitudinalgrooves 371 extending from its proximal end, and a pair of shoulders 377connecting the tubular body 370 with a distal part which comprisesvarious engagement elements. From the shoulders 377 project two legs 372which are adapted to move in the tubular clearance 389. Each leg 372 hasa foot section, the bottom of which constitutes a contact sole 374. Thedistal part of the driver 310 further comprises two slider elements 373adapted to travel the guide surfaces of the guide member 320. One of theslider elements 373 is provided with a catch element 375. A toothengaging element 376 is placed circumferentially between the two sliderelements 373 and are rigidly connected to them such that the toothengaging element 376 undergoes the same translational and/or rotationalmovement as the slider elements 373, and vice versa.

During dose setting the tooth engaging element 376 is able to performaxial relative motion with respect to the piston rod 307, whereas duringinjection the tooth engaging element 376 is adapted to move into contactwith a tooth 319 on the piston rod 307 and move the piston rod 307axially a distance through the housing 302. The shoulders 377 act as abearing face for the spring 311 and are thereby the physical interfacefor the exchange of axial forces between the spring 311 and the driver310. Adjacent one of the shoulders 377 is an abutting surface 378adapted to abut with the distal end of the spring 311 for the exchangeof torques between the spring 311 and the driver 310.

FIG. 12 is a two-dimensional representation of the guide member 320 andthe driver 310, showing one of the slider elements 373 in two differentpositions on the guide member 320. It is understood that the guidemember 320 comprises two sets of guiding surfaces which the two sliderelements 373 travel simultaneously. However, as this movement of theslider elements 373 along the respective guiding surfaces is identicalonly one of them is presented. The dose shelf 323 and the longitudinalguide surface 324 are mutually connected at an angle 8. The connectionpoint between the dose shelf 323 and the longitudinal guide surface 324can be termed a ramp edge 328 and it constitutes a transition pointbetween sliding motion of the slider element 373 along the longitudinalguide surface 324 and sliding motion of the slider element 373 along thesloping dose shelf 323. The spiralling motion of the slider element 373along the dose shelf 323 is limited by the stop surface 322 and theaxial motion of the slider element 373 along the longitudinal guidesurface 324 is limited by the end of dose stop 325. The axial length ofthe longitudinal guide surface 324 is H, i.e. when the slider element373 is positioned exactly at the ramp edge 328 it is lifted a distance Hfrom the end of dose stop 325. Due to the slope of the dose shelf 323 inaddition to a rotational movement the slider element 373 also performsan axial movement, D, when it travels the dose shelf 323 from the rampedge 328 to the stop surface 322. When the slider element 373 ispositioned at the stop surface 322 it is thus lifted an axial distanceequalling H+D from the end of dose stop 325. The axial dimension H+D isnotably larger than the distance between two consecutive teeth 319 onthe piston rod 307, which is again larger than, or equal to, the axialdimension H.

Due to the torsionally pre-tensioned spring 311, the slider element 373is biased against the stop surface 322 when it is positioned on the doseshelf 323 and against the longitudinal guide surface 324 when it ispositioned at the end of dose stop 325 (it is in fact biased against thelongitudinal guide surface 324 at any position below the ramp edge 328).The spring 311 is also axially pre-tensioned biasing the slider element373 towards the end of dose stop 325. The characteristics of the spring311 and the slope of the dose shelf 323 are, however, dimensioned suchthat when the slider element 373 is positioned above the ramp edge 328the torque provided by the spring 311 is able to overcome the axialforce of the spring 311 and the slider element 373 will be forcedtowards the stop surface 322.

FIG. 13 is a two-dimensional representation of the guide member 320 andthe driver 310 in a variant where the guide member 320 further comprisesa support shelf 321 for supporting the slider element 373 prior to thefirst use of the injection device 300. Due to the biasing torque of thespring 311 the slider element 373 is secured on the support shelf 321until the device is taken into use. The slider element 373 is capable ofsliding along the support shelf 321 and the stop surface 322 to take upa position on the dose shelf 323 in a manner similar to its movementfrom the dose shelf 323 to the end of dose stop 325. The slider element373 is, however, not able to move from the dose shelf 323 back to thesupport shelf 321, i.e. once the slider element 373 has been transferredaway from the support shelf 321, it can only move between the dose shelf323 and the end of dose stop 325. The axial length of the stop surface322 is P, i.e. the slider element 373 travels the axial distance P whenmoved from the support shelf 321 to the dose shelf 323. Since P is,relatively, much smaller than H, and there may further be a small axialclearance between the piston rod 307 and the piston 308 when theinjection device 300 is supplied by the manufacturer, when the injectiondevice 300 is used for the first time the piston rod 307 will perform amuch smaller axial movement than during subsequent uses, therebyenabling an initial priming that does not waste an approximately fulldose of the liquid drug.

FIG. 14 is a perspective view of the injection button 305 comprising apush face 352 for interfacing with an operator of the injection device300. The injection button 305 further comprises two flanges 353, eachprovided with a helical track 351 and two flange sides 354.

FIG. 15 is a perspective view of the coupling ring 330 adapted to couplethe injection button 305 and the driver 310. The coupling ring 330 has aproximal face 331 and a distal face 332 and two radially oppositetongues 333 adapted to engage with the grooves 371 in the tubular body370 of the driver 310 to rotationally lock the coupling ring 330 to thedriver 310. The tongues 333 are further adapted to engage with thespring base 360 to translationally lock the coupling ring 330 to thespring base 360. The coupling ring 330 and the driver 310 are able toperform relative translatory motion limited by the length of the grooves371. Two protrusions 334 are provided to engage with, and travel, thehelical tracks 351 in the flanges 353 to thereby transform rotationalmotion of the coupling ring 330 to translational motion of the injectionbutton 305, and vice versa.

FIG. 16 is a perspective view of the spring base 360 which is adapted tohold one end of the spring 311 in a permanent position with respect tothe housing 302. The spring base 360 has two radially opposite arms 364each comprising a hook 362 for engagement with the respective apertures361 in the housing 302, and two contact faces 365 adapted to abut withthe flange sides 354, thereby preventing the injection button 305 fromrotating relative to the spring base 360. Due to the engagement betweenthe hooks 362 and the apertures 361 the spring base 360 is completelylocked to the housing 302, i.e. the spring base 360 is prevented fromperforming rotational as well as translatory motion relative to thehousing 302. A spring retaining groove 366 is provided for retaining theproximal end of the spring 311. The spring base 360 further comprises aproximal face 363 adapted to abut with the distal face 332 of thecoupling ring 330, and two circumferential grooves 367 adapted toslidably engage with the tongues 333 and to retain the tongues 333 withrespect to axial movement. The coupling ring 330 is therebytranslationally locked to the spring base 360, but capable of rotatingrelative thereto, the rotational motion being limited by thecircumferential dimension of the grooves 367.

FIG. 17 is a perspective view showing an assembly of the driver 310, thespring 311, and the spring base 360. The proximal spring end 397 isretained in the spring base 360 and the distal spring end 398 is inconnection with the driver 310. As the spring base 360 is locked to thehousing 302 and thereby unable to move the torsionally pre-tensionedspring 311 will bias the driver 310 anti-clockwise, as seen from thespring base 360.

FIG. 18 is a perspective view illustrating the functional connectionbetween the injection button 305 and the driver 310. A push on the pushface 352 will force the injection button 305 downwards towards thespring base 360. As the injection button 305 is locked against rotationrelative to the spring base 360 this downwards movement is purelytranslational. During the translational movement of the injection button305 the protrusions 334 travel the helical tracks 351. This engagementconverts the movement of the injection button 305 to a rotationalmovement of the coupling ring 330, and since the coupling ring 330 isrotationally locked to the driver 310, also the driver 310 will rotate.The helical tracks 351 are arranged such that when the injection button305 is pushed towards the spring base 360 the coupling ring 330, andthereby the driver 310, will rotate clockwise, as seen from the springbase 360, i.e. against the rotational bias of the spring 311.

FIG. 19 is a perspective view of the injection device 300 with thehousing 302 removed, showing an interaction between the driver 310 andthe cap 315 when the cap 315 is mounted on the injection device 300 tocover and protect the distal part of the injection device 300. For thesake of clarity the proximal end 344 of the cartridge holding part 303has been removed from the figure. When the cap 315 is completelyreceived in the cap receiving part 309 an annular abutting surface 381on the cap 315 abuts the distal housing edge 385, and a cap edge 382abuts the contact soles 374 of the driver 310. This corresponds to asituation where the injection device 300 is loaded, i.e. a dose has beenset. As long as the injection device 300 still contains enough liquiddrug to provide a full dose the injection button 305 will in such asituation protrude from a proximal housing opening 384. In FIG. 19,however, the injection button 305 is depressed against the spring base360. This illustrates a situation where a user has tried to activate theinjection mechanism to eject the set dose from the cartridge 304 whenthe cap 315 is mounted on the injection device 300. In such a casedepressing the injection button 305 will still cause a rotation of thedriver 310 against the biasing torque of the spring 311, but since thecap edge 382 blocks against translational movement of the driver 310 viathe interface with the contact soles 374 the contact soles 374 will justslide along the cap edge 382 and no ejection will take place. When theuser removes the push force from the injection button 305 the biasingtorque of the spring 311 will force the driver 310 to rotate in theopposite direction until the slider elements 373 meet the respectivestop surfaces 322 (not visible). During this movement the contact soles374 will slide along the cap edge 382 back to their original positionson the cap edge 382, and the injection button 305 will be forced toproject out of the proximal housing opening 384 due to the threadedengagement with the coupling ring 330. Apertures 383 in the cap 315 areadapted to receive respective beads (not shown) on the cartridge holdingpart 303 to ensure that the cap 315 is able to withstand a certain pushforce from the contact soles 374 due to the translational bias of thespring 311 when the driver 310 is rotated to a position corresponding tothe slider elements' 373 passage of the ramp edges 328 (not visible).

FIG. 20 is a perspective view of an end-of-content mechanism in theinjection device 300. In FIG. 20 the tooth engaging element 376 haspassed the most proximal positioned tooth 390 on the piston rod 307 andslaved the piston rod 307 to cause an injection of the last remainingfull dose in the cartridge 304, and the driver 310 has responded to aremounting of the cap 315 by moving proximally with respect to thepiston rod 307. As long as more doses remain in the cartridge 304repositioning the cap 315 in the cap receiving part 309 will lead toboth a translatory and a rotational movement of the driver 310, as willbe explained in greater detail below. However, when the last full dosehas been injected repositioning the cap 315 in the cap receiving part309 will only lead to a translatory movement of the driver 310 due tothe construction of the proximal end of the piston rod 307 and thedistal part of the respective slider elements 373. The stop face 393 atthe proximal end of the piston rod 307 is adapted to abut with the catchelement 375 to prevent anti-clockwise rotation of the driver 310 withrespect to the piston rod 307. Further, the longitudinal track 394 (notvisible) is adapted to receive a protrusion 379 to thereby prevent thedriver 310 from rotating with respect to the piston rod 307. Theprotrusion 379 is received in the longitudinal track 394 at the sametime as the catch element 375 engages with the stop face 393, and thestop face 393 and the longitudinal track 394 thus reinforce each othersindividual restriction of the freedom of movement of the driver 310.

Operation of the Injection Device Represented by FIGS. 7-20

In the following a situation of use of the injection device according tothe fourth embodiment of the invention, as depicted in FIGS. 7-20, willbe described. The injection device 300 shown in FIG. 7 is in a non-usestate having the cap 315 mounted thereon. When the user needs to performan injection he/she removes the cap 315 from the injection device 300and attaches an injection needle to the needle hub interface 343. Theinjection device 300 is already loaded and ready to inject the set doseso the user simply selects the injection site, positions the injectionneedle in the skin and pushes the injection button 305 which protrudesfrom the housing opening 384 at the proximal end of the housing 302.Pushing the injection button 305 in the distal direction towards thehousing 302 causes a substantially pure translatory displacement of theinjection button 305 relative to the housing 302 due to the contactfaces 365 preventing rotation of the injection button 305 via theengagement with the flange sides 354. This translatory displacement ofthe injection button 305 causes the protrusions 334 to travel thehelical tracks 351. Since the coupling ring 330 is axially locked withrespect to the housing 302, due to the engagement between the tongues333 and the circumferential grooves 367 in the spring base 360 beingcompletely locked with respect to the housing 302, when the protrusions334 travel the helical tracks 351 the translatory movement of theinjection button 305 is transformed into a rotational movement of thecoupling ring 330 relative to the housing 302. The engagement betweenthe tongues 333 and the longitudinal grooves 371 in the tubular body 370forces the driver 310 to rotate along with the coupling ring 330.

The rotation of the driver 310 caused by the depression of the injectionbutton 305 is performed against the biasing torque of the spring 311. Inthe situation where the user has not yet depressed the injection button305 the slider elements 373 rests on the respective dose shelves 323being biased against the stop surfaces 322 by the spring torque.Depressing the injection button 305, and thereby causing a rotation ofthe driver 310, will lead to the slider elements 373 being slid down thedose shelves 323 towards the ramp edges 328. When the injection button305 is substantially fully depressed in the housing 302 the sliderelements 373 reach the transition point at the ramp edges 328 at whichpoint the spring 311 will release its stored translational energy andforce the slider elements 373, via the abutment with the shoulders 377on the driver 310, down along the longitudinal guide surfaces 324towards the end of dose stop 325. During the movement of the sliderelements 373 along the longitudinal guide surfaces 324 the toothengaging element 376, being in engagement with a tooth 319 of the pistonrod 307, will move along and thereby force the piston rod 307 to performa corresponding axial forward movement through the central bore 380.Since the piston rod 307 is connected to the piston 308 such a forwardmovement of the piston rod 307 will cause a corresponding advancement ofthe piston 308 in the cartridge 304, leading to the ejection of the setdose from the cartridge 304. Hence, following a substantially fulldepression of the injection button 305, the spring 311 willautomatically eject the liquid drug from the injection device 300whether or not the user keeps a pressure on the push face 352. While thepiston rod 307 moves axially to expel the set dose the tip 327 of theclick finger 326 rides over the teeth 395 of the piston rod 307 beingdistributed between two consecutive larger teeth 396, thereby providingan audible feedback mechanism indicating to the user through audibleclicks that the dosage is progressing. Just as the piston rod 307 stopsits forward movement when the slider elements 373 are at the end of dosestop 325 the tip 327 rides over a larger tooth 396 providing adistinguishable audible indication, such as a larger click sound, of thefact that the movement of the piston 308 has stopped and that the dosagein principle is completed. When the slider elements 373 are at the endof dose stop 325 the driver 310 will be positioned such in the housing302 that it completely covers the window 399, thereby also providing avisual end of dose indication. The user may then wait a few secondsbefore taking the injection needle out of the skin. However, when thishappens, all the user has to do to prepare the injection device 300 forthe next injection is to reposition the cap 315 in the cap receivingpart 309, i.e. to put the cap 315 back on the injection device 300.

Repositioning the cap 315 in the cap receiving part 309 after aninjection will cause a next dose to be set, as explained in thefollowing. Due to the threaded engagement between the injection button305 and the coupling ring 330 the injection button 305 will staydepressed in the housing 302 when the user releases the pressure fromthe push face 352 following the activation of the injection mechanism.This indicates to the user that the injection mechanism has beenactivated and that a dose is either being expelled or has been expelledfrom the cartridge 304. When the cap 315 is repositioned in the capreceiving part 309 after an injection the cap edge 382 will abut thecontact soles 374 on the legs 372 of the driver 310. As the cap edge 382during this repositioning of the cap 315 is moved gradually furthertowards the proximal end of the injection device 300 (when the annularabutting surface 381 moves towards abutment with the distal housing edge385) it will push the driver 310 in the proximal direction accordingly.The driver 310 is thereby displaced axially against the translationalbiasing force of the spring 311 as the slider elements 373 move up alongthe longitudinal guide surfaces 324 towards the ramp edges 328. When thedriver 310 is moved so far proximally by the cap edge 382 that theslider elements 373 reach the ramp edges 328 the torsional tension ofthe spring 311, having actually been increased during the injectionprocedure, will move the slider elements 373 up along the dose shelves323 to the stop surfaces 322, thereby rotating the driver 310 relativeto both the piston rod 307 and the housing 302. Since the dose shelves323 are sloped this movement of the slider elements 373 will also causethe driver 310 to perform a small additional axial movement. Themovement of the driver 310 causes the tooth engaging element 376 toperform an identical combined translatory and rotational movement,whereby it is lifted out of engagement with one tooth 391 on the pistonrod 307 to pass the next more proximally positioned tooth 392. Since theaxial displacement of the driver 310 during movement of the sliderelements 373 from the end of dose stop 325 to the stop surfaces 322,H+D, is larger than the distance between two consecutive teeth 319 onthe piston rod 307 the tooth engaging element 376 actually passes thenext tooth 392 and leaves a small space between them, as shown in FIG.18. As long as the cap 315 is positioned in the cap receiving part 309in such a way that the cap edge 382 has not yet moved the driver 310proximally to a point where the slider elements 373 have passed the rampedges 328, the tooth engaging element 376 has not passed the next tooth392, and if the cap 315 in such a situation is removed from theinjection device 300 the translational bias of the spring 311 will movethe slider elements 373 back to the end of dose stop 325, whereby thedriver 310 will return to the position it takes following an injectionand the tooth engaging element 376 will move back into engagement withthe tooth 391. In other words the injection mechanism is not activated.However, if the cap 315 is positioned in the cap receiving part 309 suchthat the cap edge 382 moves the driver 310 proximally to an extent wherethe slider elements 373 pass the transition point at the ramp edges 328the spring 311 will release its stored rotational energy and move theslider elements 373 along the dose shelves 323 to a position at the stopsurfaces 322. This rotational movement is performed against thetranslational bias of the spring 311 which means that the slope of thedose shelves 323 must be within certain limits to enable the angulardisplacement of the driver 310. In this case, the slope of the doseshelves is approximately 10°, i.e. the angle 8 is approximately 260°.

When the driver 310 is rotated due to the slider elements 373 travellingthe dose shelves 323 the tooth engaging element 376 is moved from aposition just below the next tooth 392 (corresponding to the position ofthe slider elements 373 just below the ramp edges 328) to a positionabove the tooth 392 in a combined translatory and rotational motion.This combined translatory and rotational motion is caused by the spring311 releasing its stored rotational energy when the slider elements 373pass the ramp edges 328, i.e. when this transition point is reached theuser is no longer in control of the dose setting and the dose will beset no matter if the user dismounts the cap 315 from the injectiondevice 300 or tries other maneuvers to stop it. Furthermore, thetorsional pre-tensioning of the spring 311 assures a stabile position ofthe slider elements 373 on the dose shelves 323 at the stop surfaces322, whereby the injection device 300 is also secured from being fireduntil the user activates the injection mechanism to inject the set dose.

Since the driver 310 and the coupling ring 330 are rotationally lockedthe rotation of the driver 310 in connection with the dose being setcauses the coupling ring 330 to rotate along, whereby the protrusions334 will travel the helical tracks 351 in the injection button 305 andcause the injection button 305 to translate out of the proximal housingopening 384. As the driver 310 only rotates when the slider elements 373have passed the ramp edges 328 and a dose is actually being set, theinjection button 305 will only protrude from the housing 302 when a doseis set. This gives a clear signal to the user that either no dose is setor a dose is set and the injection device is ready for injection. Inother words, when the cap 315 is mounted properly on the injectiondevice 300 a dose is automatically set by the injection device 300 andthe injection button 305 is automatically moved out of the housing 302to indicate that the device is ready for use.

When the cap 315 is mounted on the injection device 300 it is notpossible to activate the injection mechanism to eject a dose out of thereservoir 304. This will be explained in the following. As mentionedabove, when positioning the cap 315 in the cap receiving part 309 thecap edge 382 will abut the contact soles 374 and move the driver 310proximally in the housing 302. This action will move the driver 310 awayfrom the window 399, and when the slider elements 373 are secured on thedose shelves 323 and a dose is set, the user can not see the driver 310through the window 399. As long as the cap 315 is mounted on theinjection device 300 the cap edge 382 abuts the contact soles 374. Ifthe user tries to activate the injection mechanism by pressing theinjection button 305 towards the housing 302, he/she will beunsuccessful because the cap edge 382 prevents any advancement of thepiston rod 307 through the housing 302. The injection button 305 is freeto move towards the housing 302. As the injection button 305 movestowards a depressed state the coupling ring 330 will rotate and thiswill cause the driver 310 to rotate against the rotational bias of thespring 311, as explained above in connection with an injectionprocedure. However, instead of moving down the sloping dose shelves 323the slider elements 373 will just rotate while maintaining the sameaxial position. This is due to the contact soles 374 sliding along thecap edge 382 and not being able to perform an axial movement. When theinjection button 305 is fully depressed in the housing 302 the driver310 has been subjected to an angular displacement corresponding to adisplacement of the slider elements 373 from the position on the doseshelves 323 at the stop surfaces 322 to a position past the ramp edges328, at a height H+D above the end of dose stop 325. If the userreleases the pressure from the injection button 305 the torsionallypre-tensioned spring 311 will immediately force the driver 310 toperform a reverse rotation. This is possible since the slider elements373 are positioned above the ramp edges 328, and when the driver 310rotates so does the coupling ring 330. The reverse rotation of thecoupling ring 330 then causes the injection button 305 to travel out ofthe housing opening 384 and back to its most proximal positionindicating that a dose is set and the injection device 300 is ready forinjection. In other words, the user is able to press the injectionbutton 305 against the housing 302 when the cap 315 is mounted on theinjection device 300 without this leading to any drug being expelledfrom the reservoir 304. And when the user releases the pressure from theinjection button 305, the injection device 300 will automatically pushthe injection button 305 back out of the housing 302 due to the spring311 releasing stored energy for rotational reverse motion of the driver310. When the slider elements 373 are at the position above the end ofdose stop 325, i.e. on the other side of the ramp edges 328, thetranslational bias of the spring 311 will try to force the driver 310axially in the distal direction against the contact force from the capedge 382. The spring 311 is however not capable of moving the cap 315out of the cap receiving part 309 due to the engagement between the cap315 and the cap receiving part 309. Furthermore, beads (not shown) onthe cartridge holding part 303 engage with the apertures 383 in the cap315 to reinforce the connection. An injection device is thereby providedwhich is incapable of ejecting drug out of the reservoir when capped,while at the same time allowing the injection button to move freely inand out of the housing.

When the injection device 300 has been used for injection a number oftimes and the last full dose has just been ejected out of the cartridge304 the tooth engaging element 376 is in engagement with the mostproximal tooth 390 on the piston rod 307. If the user puts the cap 315back on the injection device 300 the cap edge 382 will, as beforeexplained, move the driver 310 proximally in the housing 302 whereby thetooth engaging element 376 will be lifted out of engagement with thetooth 390. However, as the slider elements 373 approach the transitionpoint at the ramp edges 328, the catch element 375 engages with the stopface 393 and the protrusion 379 slides into the longitudinal track 394.The driver 310 is thereby prevented from rotating with respect to thepiston rod 307. Since the piston rod 307 is rotationally locked in thecentral bore 380 it is not able to rotate with respect to the housing302. The driver 310 is therefore in this particular situation not ableto rotate relative to the housing 302. As the driver 310 and thecoupling ring 330 are rotationally locked the coupling ring 330 willalso not rotate and the injection button 305 is thus not moved out ofthe housing opening 384. This is a clear signal to the user that thelast dose has been injected and the injection device 300 is empty.

It is clear from the above description that the transition point at theramp edges 328 constitutes a boundary between manual and automaticactions in the respect that during dose setting all that happens beforethe slider elements 373 reach the ramp edges 328 is in the hands of theuser, whereas when the slider elements 373 pass the ramp edges 328 theinjection device 300 will take over and automatically set the dose andsecure the injection mechanism, while during injection all that happensas long as the slider elements 373 are positioned on the dose shelves328 is in the hands of the user, whereas when the slider elements 373pass the ramp edges 328 the injection device 300 will perform anautomatic injection which can not be aborted.

FIGS. 21-30 show an injection device 400 according to a fifth embodimentof the invention. The injection device 400 is operationally identical tothe injection device 300 and it generally includes the same features asthat device. However, there are certain structural differences betweenthe two which will be clear from the below description.

FIG. 21 is a cross sectional view of the injection device 400 whichcomprises a housing 402, a cartridge 404 containing a liquid drug, acartridge holding part 403, a cap receiving part 409 and a cap 415. Theliquid drug is positioned between a piston 408, which is capable ofmoving axially in the cartridge 404, a tubular cartridge wall 440, and aself-sealing septum 442 covering a drug outlet 441. An injection needle406 is attached to the injection device 400 via a needle hub interface443. An axially moveable piston rod 407 is coupled to the piston 408 viaa piston rod foot 447. The piston rod 407 is adapted to be moved axiallyby a driver 410. A guide member 420 guides the movement of the driver410 and the piston rod 407. The injection device 400 is powered by arotationally pre-stressed spring 411 which is locked to the housing 402at its proximal end, via a spring base 460, and which is coupled to thedriver 410 at its distal end. The spring base 460 further holds thedistal end of a button spring 450 adapted to bias an injection button405 towards a position in which it protrudes from the proximal end ofthe housing 402.

FIGS. 22 and 23 show the guide member 420 in more detail. The guidemember 420 comprises a dose shelf 423 adapted to support and guide thedriver 410 during the second part of the dose setting procedure and thefirst part of the injection procedure. A longitudinal guide surface 424leads from the dose shelf 423 to an end of dose stop 425. The dose shelf423 is a helical ramp segment which extends circumferentially from aconnection with the longitudinal guide surface 424 to a longitudinalstop surface 422. It is to be understood, that radially opposite thisset of guide surfaces is a similar set of guide surfaces. This set is,however, not visible on the figures. A click finger 426 is provided onthe guide member 420 for engagement with the piston rod 407. A tubularclearance 489 is provided between an outer wall 429 of an inner tubularstructure of the guide member 420 and the wall of the guide member 420.Two radially opposite guide elements 436 are adapted to engage thethrough-going piston rod 407 (not shown) and guide the axial movementsof the piston rod 407 while preventing the piston rod 407 from rotatingrelative to the housing 402. A distal edge 485 of the guide member 420is adapted to abut the cap 415 when the cap 415 is engaged in the capreceiving part 409.

FIG. 24 shows the driver 410 which comprises a tubular body 470, acouple of pushing surfaces 469, two slider elements 473 adapted totravel the guide surfaces of the guide member 420, two contact soles474, and a tooth engaging element 476 adapted to engage with teeth onthe piston rod 407 in order to slave the piston rod 407 in a forwardmotion towards the distal end of the injection device 400. A catchelement 475 is further provided for engagement with the proximal end ofthe piston rod 407 after the last full dose has been delivered from thecartridge 404.

FIG. 25 shows the injection button 405 comprising a push face 452 forinterfacing with an operator of the injection device 400. The injectionbutton 405 further has two sets of flanges 453, 455 each provided withpushing surfaces 416 for sliding engagement with the pushing surfaces469 on the driver 410. The flanges 455 are each provided with a hook 456adapted to engage with respective catch members (not shown) in thehousing 402 for holding the injection button 405 depressed in thehousing 402 against the bias of the button spring 450 when the injectionmechanism has been activated to inject a set dose. The flanges 453 areeach provided with a longitudinal slit 457 adapted to engage withrespective protrusions (not shown) in the housing 402 therebyrotationally locking the injection button 405 with respect to thehousing 402. The protrusions (not shown) in the housing 402 are capableof axially travelling the slits 457, whereby the injection button 405 isable to move axially relative to the housing 402 a distance determinedby the axial dimension of the longitudinal slits 457.

FIG. 26 illustrates the functional connection between the injectionbutton 405 and the driver 410. The shown assembly has been separatedfrom the rest of the injection device for the sake of clarity. When theuser depresses the injection button 405 by pushing on the push face 452the pushing surfaces 416 move into engagement with the pushing surfaces469 on the driver 410. The purely translational movement of theinjection button 405 causes the pushing surfaces 469 to slide along thepushing surfaces 416 whereby the driver 410 is rotated clockwise withrespect to the injection button 405 (and the housing 402). In aninjection situation this will lead to the tooth engaging element 476moving into engagement with a tooth on the piston rod 407, and when theslider elements 473 pass the transition point at the ramp edges 428 thespring 411 will force the driver 410, and thereby the tooth engagingelement 476 and the piston rod 407, to advance axially in the distaldirection to inject the set dose. The interface between the injectionbutton 405 and the driver 410 works both ways, i.e. if the driver 410 isrotated anti-clockwise, e.g. during a dose setting, the pushing surfaces469 will slide along the pushing surfaces 416 on the flanges 453, 455,whereby the injection button 405 will be released from its retainedposition and displaced axially out of the housing 402 by the buttonspring 450.

FIG. 27 depicts the situation where the tooth engaging element 476 hasbeen moved from one tooth 491 to a more proximally positioned tooth 492during a dose setting. The shown assembly has been separated from therest of the injection device for the sake of clarity. This hasartificially uncovered the proximal spring end 497 which is actuallyretained in the spring base 460.

FIG. 28 depicts the situation where the slider elements 473 arepositioned on the dose shelves 423 at the stop surfaces 422 (notvisible) and the injection device is ready for injection. Again theshown assembly has been separated from the rest of the injection devicefor the sake of clarity. A push on the injection button 405 (not shown)will cause the driver 410 to rotate clockwise (as seen from theinjection button) against the rotational bias of the spring 411. At thepassage of the ramp edges 428 the slider elements 473 will be forcedalong the longitudinal guide surfaces 424 towards the end of dose stop425.

FIG. 29 illustrates an end of content situation. When the last full dosehas been delivered from the injection device 400 and the userrepositions the cap 415 in the cap receiving part 409 to thereby movethe driver 410 proximally in a manner similar to what has previouslybeen described in relation to the injection device 300 the toothengaging element 476 is moved out of engagement with the most proximalpositioned tooth 490 and up along the piston rod 407. This movement isperformed synchronously with the movement of the slider elements 473 upalong the longitudinal guide surfaces 424. However, as the sliderelements 473 approach the transition point at the ramp edges 428, thecatch element 475 engages with the stop face 493 and the driver 410 isthereby prevented from rotating with respect to the piston rod 407.Since the piston rod 407 is rotationally locked to the housing 402 thedriver 310 is in this particular situation not able to rotate relativeto the housing 402. In any previous case, when the user has repositionedthe cap 415 in the cap receiving part 409 following an injection and thedriver 410 has been moved proximally such that the slider elements 473have passed the ramp edges 428 and a dose thereby has been set, the lastpart of the dose setting has been performed automatically by the spring411 releasing its stored energy for rotational motion of the driver 410.This rotation of the driver 410 has caused a simultaneous translation ofthe injection button 405 due to the interface between the pushingsurfaces 469, 416 deflecting the hooks 456 out of engagement with thecatch members (not shown) in the housing 402 thereby releasing thebutton spring 450 and consequently forcing the injection button 405 outof the housing 402, signalling to the user that a dose has been set andthat the device is ready for the next injection.

As the driver 410 is incapable of rotation when the cap 415 is mountedon the injection device 400 after injection of the last full dose, thebutton spring 450 will not be released and the injection button 405 willtherefore not be moved out of the housing 402. This is a signal to theuser that the injection device 400 has been emptied.

FIG. 30 is a perspective view of the injection device 400 with thehousing 402 removed, showing an interaction between the driver 410 andthe protective cap 415. The figure illustrates a situation where theuser tries to eject a dose from the cartridge 404 (not visible) whilethe cap 415 is mounted on the injection device 400. The basic movementpattern is similar to that described in relation to FIG. 19, the onlyreal difference being the action of the button spring 450 which realisesthe proximal movement of the injection button 405. A cap edge 482 abutsthe contact soles 474 and prevents the driver 410 from undergoing axialdisplacement towards the distal end of the injection device 400.Depressing the injection button 405 causes the contact soles 474 toslide along the cap edge 482, whereby the tooth engaging element 476 isprevented from moving into contact with a tooth 419 on the piston rod407. The rotational bias of the spring 411 will pose a return torque onthe driver 410 which will again release a locking of the button spring450 due to the interaction between the pushing surfaces 469 and theflanges 453, 455. When the cap 415 is properly positioned in the capreceiving part 409 an annular abutting surface 481 abuts the distal edge485 of the guide member 420. A couple of beads 488 on the cap 415 areadapted to engage with a bead receiving track on the inside wall of theguide member 420 for leading the cap 415 properly onto the injectiondevice 400.

FIG. 31 is a cross sectional view of an injection device 500 accordingto a sixth embodiment of the invention, in a loaded state, i.e. where adose is set. The injection device 500 comprises a housing 502, acartridge 504 with a piston 508, a cap 515, a toothed piston rod 507, adriver 510 comprising a tooth engaging element 576 adapted to engage atooth 519 on the piston rod 507 and slave the piston rod 507 towards theneedle end of the injection device 500. The driver 510 further comprisesradially deflectable snap arms 512 adapted to engage with respectiveprotrusions 587 on the housing 502. The snap arms 512 are elasticallybiased towards the inside wall of the housing 502. A main spring 511 isprovided for powering the driver 510 during injection, and a secondaryspring 550 is provided for biasing an injection button 505 towards aposition in which it protrudes from the proximal end of the housing 502.The injection button 505 has longitudinally extending arms 558 ending inrespective hooks 556 adapted to engage with radially protruding catchelements 546 to hold the injection button 505 in a depressed position inthe housing 502 against the bias of the secondary spring 550. Theinjection device 500 further has an injection needle 506 attached.

FIGS. 32 a-c show an injection button release mechanism of the injectiondevice 500 in detail. In FIG. 32 a the injection button 505 is depressedin the housing 502 illustrating a situation where the user has performedan injection. The injection button 505 is held in this position againstthe biasing force of the secondary spring 550 due to the engagementbetween the hooks 556 and the catch elements 546.

In FIG. 32 b the driver 510 has been displaced proximally in the housing502 due to the user mounting the cap 515 on the injection device 500.This has caused inclined push faces 548 of the snap arms 512 to slidealong corresponding inclined faces 549 of the protrusions 587 and moveinto contact with corresponding inclined push faces 559 of the hooks556. Further proximal movement of the driver 510, and thereby the snaparms 512, will cause the inclined push faces 548 of the snap arms 512 toslide along the inclined push faces 559 of the hooks 556, whereby thehooks 556 will be moved out of engagement with the catch elements 546.When the hooks 556 are moved completely out of engagement with the catchelements 546 three things happen simultaneously. The secondary spring550 releases its stored energy and forces the injection button 505proximally out of the housing 502, and the snap arms 512 deflect backtowards the inside wall of the housing 502 to move into engagement withthe proximal faces of the protrusions 587, thereby cocking the mainspring 511. This is shown in FIG. 32 c. Furthermore, the tooth engagingelement 576 passes a more proximally positioned tooth 519 on the pistonrod 507, whereby a dose is set.

When the user pushes the injection button 505 to inject a set dose thearms 558 are moved distally in the housing 502 while being deflectedradially outwards by a sliding engagement with the catch elements 546.The inclined push faces 559 of the hooks 556 are hereby brought intoengagement with the inclined push faces 548 of the snap arms 512. As theinjection button 505 is being fully depressed against the housing 502the arms 558 will force the inclined push faces 548 of the snap arms 512to slide along the inclined push faces 559 of the hooks 556 to a pointwhere the snap arms 512 are moved out of engagement with the protrusions587. This will cause the main spring 511 to release its stored energyand move the driver 510 distally in the housing 502 to expel the dose ofdrug through the injection needle 506. Simultaneously, the elasticrecovery of the arms 558 will cause the hooks 556 to move intoengagement with the catch elements 546, thereby cocking the secondaryspring 550 and retaining the injection button 505 within the housing502.

1. An injection device for administering apportioned doses of liquiddrug, the injection device comprising: a housing, a reservoir forholding the drug, a piston adapted to move axially in the reservoir,dose setting means operable to set a dose, injection means operable toinject the set dose and comprising a piston rod for sequentiallyadvancing the piston in the reservoir to expel a volume of the liquiddrug, a push button operatively coupled to the dose setting means andthe injection means and axially moveable between a first position inwhich the dose is set and a second position in which the injection meanshas been activated to inject the set dose, and retaining means forholding the push button in the second position when the injection meanshas been activated to inject the set dose, wherein the retaining meansis operatively coupled to the dose setting means in such a manner thatwhen the dose setting means is operated to set a dose the retainingmeans is automatically disabled.
 2. An injection device as in claim 1,wherein when the dose setting means is operated to set a dose, the pushbutton is automatically moved from the second position to the firstposition.
 3. An injection device as in claim 2, wherein the push buttonis moved from the second position to the first position by a forcetransmitting member activating the push button via a translationaland/or rotational movement.
 4. An injection device as in claim 1 furthercomprising energy means acting on the push button to bias the pushbutton towards the first position.
 5. An injection device as in claim 4,wherein the energy means comprises a spring.
 6. An injection device asin claim 1, wherein the movement of the push button from the secondposition to the first position is purely translational.
 7. An injectiondevice as in claim 1, wherein the movement of the push button from thefirst position to the second position is purely translational.
 8. Aninjection device as in claim 1, wherein the retaining means comprises asnap fit between the push button and the housing.
 9. An injection deviceas in claim 8, wherein the push button comprises a catch member adaptedto engage with a protuberance on the housing.
 10. An injection device asin claim 9, wherein the snap fit is disabled by a force transmittingmember having an abutment surface adapted to slideably abut with anabutment surface on the catch member to thereby move the catch memberout of engagement with the protuberance.
 11. An injection device as inclaim 3, wherein the retaining means comprises a friction fit betweenthe push button and the housing.
 12. An injection device as in claim 1,further comprising a drive member adapted to undergo relative motionwith respect to the piston rod during dose setting and to transmit adriving force to the piston rod during injection, the drive membercomprising force transmitting means.
 13. An injection device as in claim12, wherein the push button and the drive member are operatively coupledin such a manner that a rotational or spiralling movement of the drivemember causes an axial movement of the push button, and vice versa. 14.An injection device as in claim 12 further comprising a coupling elementadapted to engage with the drive member and the push button.
 15. Aninjection device as in claim 14, wherein the push button and thecoupling element are coupled via a threaded interface.
 16. An injectiondevice as in claim 15, wherein the push button comprises a helical tracksegment and the coupling element comprises a protuberance adapted toengage with and travel the helical track segment.
 17. An injectiondevice as in claim 16, wherein the retaining means comprises theengagement between the push button and the coupling element.
 18. Aninjection device as in claim 13, wherein the piston rod comprises astructural element adapted to engage with the drive member to preventthe drive member from rotating when the remaining amount of drug in thereservoir is insufficient to provide another full dose, thereby alsopreventing the dose setting means from setting a dose.
 19. An injectiondevice as in claim 13, wherein the piston rod comprises a structuralelement adapted to engage with the drive member to prevent the drivemember from rotating when the remaining amount of drug in the reservoiris insufficient to provide another full dose, thereby also preventingmovement of the push button from the second position to the firstposition.
 20. An injection device as in claim 1, further comprising: aremovable cap, and a cap receiving part adapted to abut or engage withthe cap when the cap is mounted on the injection device, wherein the capreceiving part is operatively coupled to the dose setting means in sucha manner that mounting the cap on the injection device automaticallydisables the retaining means and moves the push button from the secondposition to the first position.
 21. An injection device foradministering apportioned doses of liquid drug, the injection devicecomprising: a reservoir adapted to hold the drug, a piston adapted tomove axially in the reservoir, dose setting means operable to set adose, injection means operable to inject the set dose and comprising apiston rod for sequentially advancing the piston in the reservoir toexpel a volume of the liquid drug, a removable cap, a cap receiving partadapted to abut or engage with the cap when the cap is mounted on theinjection device, wherein the injection means is operatively coupled tothe cap receiving part in such a manner that mounting the cap on theinjection device disables the injection means, thereby preventing anejection of drug from the reservoir.
 22. An injection device as in claim21, wherein dismounting the cap from the injection device enables theinjection means, thereby allowing an ejection of drug from thereservoir.
 23. An injection device as in claim 21, wherein the cap ismounted on and/or dismounted from the injection device in asubstantially linear movement.
 24. An injection device as in claim 21,wherein the cap is mounted on and/or dismounted from the injectiondevice in a rotational or spiralling movement.
 25. An injection deviceas in claim 21, wherein when the cap is mounted on the injection devicethe piston rod is prevented from axial movement.
 26. An injection deviceas in claim 21, further comprising a drive member adapted to transmit adriving force to the piston rod during injection, wherein when the capis mounted on the injection device the drive member is capable ofperforming rotational motion, but prevented from performingtranslational motion, with respect to the cap.
 27. An injection deviceas in claim 26, wherein the drive member abuts the cap when the cap ismounted on the injection device.
 28. An injection device as in claim 26,further comprising means for holding the cap on the injection deviceagainst a translational force from the drive member.
 29. An injectiondevice as in claim 26, further comprising an injection buttonoperatively coupled to the dose setting means and the injection meansand axially moveable between a first position corresponding to aposition in which the dose is set and a second position corresponding toa position in which the injection means has been activated to inject theset dose, wherein when the cap is mounted on the injection device theinjection button is able to move between the first position and thesecond position.
 30. An injection device as in claim 29, furthercomprising energy means operatively coupled to the dose setting meansand the injection means and adapted to store and release energy fortranslational and rotational motion.
 31. An injection device as in claim29, wherein applying a force to move the injection button from the firstposition to the second position when the cap is mounted on the injectiondevice causes the drive member to rotate while the energy means storesenergy for rotational motion.
 32. An injection device as in claim 31,wherein removing the force from the injection button when the cap ismounted on the injection device causes the drive member to rotate whilethe energy means releases energy for rotational motion.
 33. An injectiondevice as in claim 32, wherein the injection button is automaticallymoved from the second position to the first position when the force isremoved.
 34. An injection device as in claim 21, wherein the dosesetting means is operatively coupled to the cap receiving part in such amanner that mounting the cap on the injection device causes the dosesetting means to set a dose.